1. Field of the Invention
The present invention relates to a rotation angle detection device used mainly for detecting a rotation angle of a steering wheel of an automobile or the like.
2. Background Art
Recently, functions of an automobile have been enhanced. In such circumstances, automobiles using various rotation angle detection devices so as to detect a rotation angle of a steering wheel and using this detected rotation angle so as to perform various controls of vehicle have been increased. This rotation angle detection device is placed in an automobile in a state in which it is disposed on the rear side of a steering wheel via a rotary connector fixed to a vehicle. The rotary connector and the rotation angle detection device have a through-hole into which a steering shaft of the steering wheel is to be inserted. The rotation angle detection device detects the rotation of the steering shaft rotating in the through-holes.
Such a conventional rotation angle detection device known from, for example, Japanese Patent Unexamined Publication No. 2006-258625 is described with reference to FIG. 11.
FIG. 11 is a sectional view showing a conventional rotation angle detection device. In FIG. 11, rotation angle detection device 10 includes rotary body 1 having spur gear 1A on the outer periphery of the side surface thereof; first detector 2 having spur gear 2A on the outer periphery of the side surface thereof; and second detector 3 having spur gear 3A on the outer periphery of the side surface thereof. Spur gear 1A meshes with spur gear 2A, and spur gear 2A meshes with spur gear 3A. The number of cogs of spur gear 2A is different from that of spur gear 3A. A pair of engaging parts 1B are formed in a protruding way on the inner periphery of the center cylindrical part of rotary body 1.
Magnets 5A and 6A are placed in the center of first detector 2 and the center of second detector 3, respectively. A wiring board (not shown) having a plurality of wiring patterns on the front and rear surfaces thereof is disposed on the front side (a face perpendicular to the drawing) of first detector 2 and second detector 3 in substantially parallel therewith. Magnetic detection elements 5B and 6B are placed on the surface of the wiring board facing magnets 5A and 6A, respectively.
Magnet 5A and magnetic detection element 5B, which face each other, form first detection part 5. Similarly, magnet 6A and magnetic detection element 6B, which face each other, form second detection part 6. The wiring board includes control part 7 having an electronic component such as a microcomputer, which is coupled to magnetic detection elements 5B and 6B.
Rotary body 1, first detector 2 and second detector 3 are rotatably held in case 8 having a substantially box shape and made of insulating resin. In addition, the wiring board is also secured to the inside of case 8. Furthermore, a cover (not shown) made of insulating resin covers the front side of case 8.
Case 8 has through-hole 8A, into which a steering shaft (not shown) is to be inserted, in the center part thereof. Round-shaped attaching hole 8B and rectangular-shaped attaching hole 8C are formed on the left and right portions of case 8 symmetrically with respect to the center of through-hole 8A, that is, the rotation center of rotary body 1.
The rotary connector disposed behind the steering wheel and fixed to a vehicle has a rotary casing latched onto a steering shaft and rotating according to the rotation of the steering shaft. The pair of engaging parts 1B formed on rotation angle detection device 10 are engaged with this rotary casing. The rotary connector has pins to be inserted into attaching holes 8B and 8C formed on case 8. By inserting the pins of the rotary connector into attaching holes 8B and 8C, case 8 is fixed to the rotary connector.
Therefore, when the steering wheel is rotated, the rotary casing is rotated according to the rotation of the steering shaft. According to this, rotary body 1 whose engaging part 1B is engaged with the rotary casing is rotated.
Furthermore, first detector 2 is rotated in linked motion with the rotation of rotary body 1, and second detector 3 is rotated in linked motion with the rotation of first detector 2. Therefore, magnets 5A and 6A placed in the centers of first and second detectors 2 and 3 are also rotated. Magnetic detection elements 5B and 6B detect the change in the magnetic force of magnets 5A and 6A as detection signals, respectively. The output data waveforms of magnetic detection elements 5B and 6B are detection signals differing in the cycle and the phase from each other because the numbers of cogs are different and the rotation speeds are also different between first detector 2 and second detector 3.
Then, control part 7 detects a rotation angle of rotary body 1, that is, a rotation angle of the steering wheel by executing a predetermined operation according to the two different detection signals and the numbers of cogs of first detector 2 and second detector 3. This detected rotation angle is output to an electronic circuit of an automobile, so that various vehicle controls are carried out.
When rotation angle detection device 10 configured as mentioned above is placed in an automobile after it is transported and stored, firstly, as mentioned above, engaging part 1B of rotary body 1 is engaged with the rotary casing of the rotary connector onto which the steering shaft is latched. Furthermore, pins formed on the rotary connector are inserted into attaching holes 8B and 8C of case 8 and placed. However, at this time, while rotation angle detection device 10 is transported, stored, and the like, rotary body 1 may be somewhat rotated. Therefore, it is necessary to carry out a so-called zero point storage with respect to control part 7 of rotation angle detection device 10.
That is to say, a rotation angle of the steering wheel is set to the neutral position of 0°, in other words, as a state in which a vehicle drives straight ahead, and the rotation angle at this time is stored in control part 7 as the neutral position of 0°. Later than this, by detecting the rotation angle of the steering wheel based on this point of zero as a reference, detection of the direction (left or right) of the steering wheel and the rotation angle (degrees) of the steering wheel is carried out.
However, in the above-mentioned conventional rotation angle detection device, when rotation angle detection device 10 is placed in an automobile, it is necessary to carry out the zero point storage with respect to control part 7 in a state in which the steering wheel is set to the neutral position of 0°. That is to say, since the operation for the zero point storage is carried out after rotation angle detection device 10 is placed in an automobile, the fabrication becomes complicated and time-consuming.